An interesting question. Especially if you imagine that ATT would sell DC Comics as a publishing entity separate from Warner Bros, then maybe typical publishing companies might be purchasers--folks like Penguin Random House or Scholastic, or maybe even some of the still existing major magazine publishing companies like Hearst, Condé Nast, or Meredith.
If you're thinking of any of the existing media companies, aside from Disney, you could sorta see Warner/DC fitting with Comcast or Sony. CBS/Viacom is trying to sell their Simon & Schuster book publisher, so they might not be a great place for DC as a publishing entity even if they go for Warner Bros. NewsCorp still has publishing (books and newspapers) but has sold Fox studios to Disney, so may not be a natural home for the whole of Warner/DC.
Beyond existing media companies, maybe some of today's major tech companies--especially with existing presence in the media space like Amazon, Netflix, and Apple--might be potential landing places for Warner/DC, but still might not be a great home for the traditional publishing part of the DC business.